Transcript CHAPTER 11 TOWARD A GREENER ANTHROSPHERE THROUGH INDUSTRIAL ECOLOGY

CHAPTER 11
TOWARD A GREENER ANTHROSPHERE THROUGH
INDUSTRIAL ECOLOGY
From Green Chemistry and the Ten Commandments of
Sustainability, Stanley E. Manahan, ChemChar Research,
Inc., 2006
[email protected]
11.1. INDUSTRIAL ECOLOGY AND INDUSTRIAL
ECOSYSTEMS
The anthrosphere has been defined as a fifth sphere of the
environment.
Industrial ecology integrates the principles of science, engineering,
and ecology in industrial systems through which goods and services
are provided in a way that minimizes environmental impact and
optimizes utilization of resources, energy, and capital
• Every aspect of the provision of goods and services from concept,
through production, and to the final fate of products remaining
after use
• A sustainable means of providing goods and services
• Most successful when it mimics natural ecosystems
Industrial Ecosystem
An industrial ecosystem functions through groups of industrial
concerns, distributors, and other enterprises functioning to mutual
advantage, using each others’ products, recycling each others’
potential waste materials, and utilizing energy as efficiently as
possible to maximize
Market value of products
Consumption of material and energy
An industrial ecosystem is illustrated on the following slide
Industrial symbiosis is the development of such mutually
advantageous interactions between two or more industrial
enterprises that cause an industrial ecosystem to develop in the first
place
• Required for recycling
Major Components of an Industrial Ecosystem Showing Maximum
Flows of Material and Energy Within the System
Scope of Industrial Ecology
Regional scope large enough to encompass several industrial
enterprises, but small enough for them to interact with each other on
a constant basis
Frequently based around transportation systems such as segments of
interstate highways
11.2. METABOLIC PROCESSES IN INDUSTRIAL
ECOSYSTEMS
Industrial metabolism refers to the processes to which materials
and components are subjected in industrial ecosystems
• Analogous to the metabolic processes that occur with food and
nutrients in biological systems
Industrial metabolism may be addressed at several levels
• Green chemistry at the molecular level where substances are
changed chemically to give desired materials or to generate energy
• Within individual unit processes in a factory
• At the factory level
• At the industrial ecosystem level
• Even globally
Wastes and Industrial Ecology
Wastes in natural and industrial ecosystems
In natural ecosystems true wastes are virtually nonexistent
• Waste plant biomass forms soil humus
Anthropospheric industrial systems have developed in ways that
generate large quantities of wastes
• Industrial waste may be defined as dissipative use of natural
resources.
• Human use of materials has a tendency to dilute and dissipate
materials and disperse them to the environment
• Materials may end up in a physical or chemical form from which
reclamation becomes impractical because of the energy and effort
required
• A successful industrial ecosystem overcomes such tendencies
Minimization of Byproduct and Waste
The objective of industrial metabolism in a successful industrial
ecosystem is to make desired goods with the least amount of
byproduct and waste
Consider production of lead from lead ore for the production of
storage batteries
• Mining large quantities of ore
• Extracting the relatively small fraction of the ore consisting of lead
sulfide mineral
• Roasting and reducing the mineral to get lead metal
• These processes generate large quantities of lead-contaminated
tailings left over from mineral extraction and significant quantities
of byproduct sulfur dioxide, which must be reclaimed to make
sulfuric acid and not released to the environment
The recycling pathway for lead production takes essentially pure
lead from recycled batteries and simply melts it down to produce
lead for new batteries
Comparison of Natural Ecosystems and Current
Industrial Systems
• The basic unit of a natural ecosystem is the organism, whereas that
of an industrial system is the firm
• Natural ecosystems handle materials in closed loops whereas with
current practice, materials traverse an essentially one-way path
through industrial systems
• Natural systems completely recycle materials, whereas in industrial
systems the level of recycling is often very low
• Organisms have a tendency to concentrate materials such as CO2
from air concentrated in biomass whereas industrial systems tend
to dilute materials to a level where they cannot be economically
recycled, but still have the potential to pollute.
• The major function of organisms is reproduction whereas the main
function of industrial enterprises is to generate goods and services
Natural Ecosystems and Current Industrial Systems
(Cont.)
• Reservoirs of needed materials for natural ecosystems are
essentially constant (oxygen, carbon dioxide, and nitrogen from air
as examples) whereas industrial systems are faced with largely
depleting reservoirs of materials (essential mineral ores)
• Recycling gives essentially constant reservoirs of materials
Regulation in Natural and Industrial Ecosystems
Biological systems have elaborate means of control.
Entire ecosystems are self-regulating.
Industrial systems do not inherently operate in a self-regulating
manner that is advantageous to their surroundings, or even to
themselves.
Failure of self-regulation of industrial systems
• Have wastefully produced large quantities of goods of marginal
value
• Running through limited resources in a short time
• Dissipating materials to their surroundings
• Polluting the environment
Industrial ecosystems can be designed to operate in a self-regulating
manner
• Best under conditions of maximum recycling in which the system
is not dependent upon a depleting resource of raw materials or
energy
Level of Recycling and Embedded Utility
High-level recycling
Low-level recycling
Product
Ass embly
Fabrication
Material
Source of raw material
Quantity of materials and energy involved
11.3. LIFE CYCLES IN INDUSTRIAL ECOSYSTEMS
In a system of industrial ecology the entire life cycle of the product
is considered as part of a life-cycle assessment.
• To determine, measure, and minimize environmental and resource
impacts of products and services.
Scope of the assessment
• Time period
•Space
• Kinds of materials, processes, and products in the assessment
Example of Scope in Life Cycle Assessment
Example of the manufacture of an insecticide that releases harmful
vapors and generates significant quantities of waste material
• A narrowly focused assessment might consider control measures to
capture released vapors and the best means of disposing of the
waste byproducts
• A broader scope would consider a different synthetic process that
might not cause the problems mentioned
• An even broader scope might consider whether or not the
insecticide even needs to be made and used; perhaps there are more
acceptable alternatives to its use.
Life Cycle Assessment
• Inventory analysis to provide information about the consumption
of material and release of wastes from the point that raw material is
obtained to make a product to the time of its ultimate fate
• Impact analysis that considers the environmental and other
impacts of the product
• Improvement analysis to determine measures that can be taken to
reduce impacts
In doing life-cycle assessments consider three major categories
• Products: Things and commodities that consumers use
• Processes: Ways in which products are made
• Facilities consisting of the infrastructural elements in which
products are made and distributed
Example of Life Cycle Assessment
Example of paper product
• The environmental impact of paper product tends to be relatively
low. Even when paper is discarded improperly; it does eventually
degrade without permanent effect.
• Process of making paper, beginning with harvesting of wood and
continuing through the chemically intensive pulping process and
final fabrication has significant environmental impact
Facilities
Highly variable impact of facilities
• Brownfields to describe sites of abandoned industrial facilities
• Challenge to decomission sites of nuclear power reactors in which
there is a significant amount of radioactivity to deal with in
dismantling and disposing of some of the reactor components
• Facilities can be designed with eventual decommissioning in mind
• Structure flexibility of commercial buildings
Product Stewardship
• Laser printer cartridges • Automobile batteries
• Disincentive of disposal fee for automobile tires
• Leasing • Deposits
11.4. KINDS OF PRODUCTS
Consumable products such as laundry detergents
Recyclable commodities such as motor oil
Service products such as washing machine
Consumable products are dispersed to the environment
• Nontoxic • Not bioaccumulative • Degradable
Recyclable commodities should be designed with durability and
recycling in mind
• Not as degradable as consumables
Service Products
Service products are designed to last for relatively long times, but
should be recyclable
• Channels through which such products can be recycled
• Proposed “de-shopping” centers where items such as old computers
and broken small appliances can be returned for recycling
• Designed and constructed to facilitate disassembly so that various
materials can be separated for recycling.
11.5. ATTRIBUTES REQUIRED BY AN INDUSTRIAL
ECOSYSTEM
Key attributes of energy, materials, and diversity
Energy
With enough energy, almost anything is possible
• Consuming abundant fossil energy resources would cause
unacceptable global warming effects
• Solar energy and wind energy are renewable sources of energy but
are intermittent nature and require large areas of land in order to
provide a significant share of energy needs
• Nuclear power facilities can provide abundant reliable energy, but
present waste problems
Cogeneration and Combined Power Cycles
Cogeneration employing combined power cycles (next slide)
represents the most efficient energy use within an industry or
within an industrial ecosystem
(1) Electricity generation
(2) Steam used in processing
(3) Steam and hot water used for heating
• Burning fuels in large turbines connected to an electrical generator
and using the hot exhaust from the turbine to raise steam can
double the overall efficiency of energy utilization.
• Using the cooled steam from the steam turbine for heating can
further increase the overall efficiency of the energy utilization
process.
Combined Power Cycles
Combined power cycles use energy with great efficiency through
several levels as shown below:
Materials
Utilization of materials
Dematerialization in which less material is used for a specific
purpose
• Example: Less copper in 12 volt automobile electrical systems
Substitution of abundant materials for scarce ones
• Solid state circuits in radios or televisions
Recycling and Waste Mining
Recycling
• Wood and paper, which are not scarce, but recycling is advisable
• Metals, especially scarce and valuable ones such as chromium,
platinum, and palladium
• Parts and apparatus that can be refurbished and reused
Waste mining: Needed materials extracted from wastes
• Combustible methane gas from municipal refuse landfills
• Aluminum from finely divided coal fly ash generated in coal
combustion
Diversity in Industrial Ecosystems
Diversity imparts a robust character to industrial ecosystems, which
means that if one part of the system is diminished, other parts will
take its place and keep the system functioning well
• Example: Diverse energy sources to reduce vulnerability to
interruptions in power and energy supplies
• Example: Diverse food sources to reduce vulnerability to reliance
on one food source for diet
The Kalundborg Industrial Ecosystem
Novo Nordisk
pharmceuticals
Gyproc
Calcium
sulfate wallboard
Sludge fertilizer
ASNAES
electrical
power plant
Cement,
road
material
Greenhouses
Cooling
water
Fuel
gas
Steam
Coal, lime
Steam heat
Homes
Fish
farm
Lake Tisso
water
Statoil
petroleum
refinery
Crude oil
Kemira
sulfuric
acid plant
11.7. ENVIRONMENTAL IMPACTS OF INDUSTRIAL
ECOSYSTEMS
The practice of industrial ecology in the anthrosphere affects the
atmosphere, hydrosphere, geosphere, and biosphere.
Emission to the atmosphere of pollutant gases, vapors from volatile
compounds, particles and greenhouse warming carbon dioxide
Large quantities of water that may become polluted or warmed
excessively when used for cooling (thermal pollution).
Disruption of the geosphere from mining, dredging, and pumping of
petroleum and other extractive activities
Detrimental effects to the biosphere by release of toxic substances
Greenhouse-warming carbon dioxide emissions, acid gas emissions,
smog-forming hydrocarbons and nitrogen oxides, and deterioration
of atmospheric quality from particles released from fossil fuel
combustion
Environmental Effects of Agricultural Activities
Some of the environmental effects of agricultural activities include
• Replacement of entire, diverse biological ecosystems with artificial
ecosystems, which causes a severe disturbance in the natural state
of the biosphere
• Loss of species diversity
• Greenhouse-warming methane from rice paddies and from
livestock digestive systems
• “Slash and burn” agricultural techniques practiced in some tropical
countries
• Water used for irrigation, water salinity
• Transgenic crops and livestock may have profound effects
Design of Industrial Ecosystems to Minimize Environmental
Impact
Recycling materials, especially those extracted from the geosphere
Selection of materials, such as silica fiber optic cables in place of
copper
Minimization of emission of volatile organic compounds
Complete water recycle
Totally eliminate wastes requiring land disposal
Most efficient use of the least polluting sources of energy possible
Design of buildings to reduce heating and cooling costs
Combined power cycles along with the generation of electricity
11.8. GREEN CHEMISTRY IN THE SERVICE OF
INDUSTRIAL ECOSYSTEMS
Percent atom economy = Total mass of product
Total mass of reactants
Use of nontoxic chemicals and processes
Consideration of the chemical reactions and processes by which
chemicals are manufactured
• Use existing chemical synthesis processes but make the process
itself safer and less polluting while also making the reagents
required for it by greener processes
• Use different reagents for the synthesis that are safer and less likely
to pollute.
Hazard Reduction
Exposure reduction has emphasized protective measures
• At a personal level, safety glasses
• At an industry level, end-of-pipe measures, such as scrubbers on
stacks
• Command and control refers to regulations that apply primarily
to processes that have inherent dangers or that produce pollutants.
• End-of-pipe measures are applied to the removal of pollutants and
wastes that are produced in a process, rather than their elimination
within the process itself.
Green chemistry relies on hazard reduction
• Know what the hazards are and where they originate
• Toxicity hazards
• Hazards associated with uncontrolled events such as fires and
explosions
Toxic Substances
Toxic substances classified according to biochemical properties that
lead to toxic responses
• Structure activity relationships, which use computer programs to
find correlations between features of chemical structure, such as
groupings of functional groups, and the toxicity of the compounds
• Example: Compounds containing the N-N=O functional group are
N-nitroso compounds, a family noted for members that cause
cancer
Chemicals to Eliminate in Reducing Toxicity Hazards
Three kinds of chemicals have a high priority in eliminating the
toxicity hazards in green chemistry
1. Heavy metals, such as lead, mercury, and arsenic (a metalloid)
2. Lipid-soluble organics that are not readily degraded and may
undergo biomagnification in moving through a food chain
3. Volatile organic compounds (VOCs, below):
H H H H H H H
H C C C C C C C H
H H H H H H H
Heptane
H
Cl
C
C
Cl
Trichloroethylene
Cl
Hazardous, Reactive Chemicals
Chemicals that pose hazards because of their potential to undergo
destructive chemical reactions
• Combustible or flammable substances
• Oxidizers, such as ammonium perchlorate, NH4ClO4, that provide
sources of oxygen for the reaction of reducers
• Reactive substances such as explosive nitroglycerin
4C3H5N3O9  12CO2 + 10H2O + 6N2 + O2 (11.8.1)
• Corrosive substances that attack materials, including even human
flesh because they are strong acids, bases, or oxidizing agents
11.9. FEEDSTOCKS, REAGENTS, MEDIA, AND
CATALYSTS
The main components of a chemical process
• Feedstocks that are converted to final product
• Reagents that act upon feedstocks
• Media in which reactions occur
• Catalysts that enable reactions to occur
Feedstocks
Three major components of the process by which raw materials from
a source are obtained in a form that can be utilized in a chemical
synthesis
1. Source of the feedstock
• Depleting resource, such as petroleum
• Recycled materials
• Renewable resources, particularly from materials made by
photosynthesis and biological processes.
2. Separation and isolation of the desired substance
• Often the most environmentally harmful because of the
relatively large amount of waste material that must be discarded
in obtaining the needed feedstock.
3. Chemical processes that give the final product by reactions upon
feedstocks by various kinds of reagents in media such as organic
solvents, often using catalysts.
Reagents
A reagent is a substance that converts feedstocks to new chemicals
• High product selectivity
• High product yield
Alternative reagents are often important in green chemistry
Oxidation and Oxidation Reagents
Oxidation reagents add oxygen to a chemical compound or a
functional group on a compound
Example:
H H
H C C OH + 2{O}
H H Ethanol
H O
H C C OH + H2O
H Acetic acid
(11.9.1)
• Oxidation often uses dangerous reagents, such as potassium
dichromate, K2Cr2O7
• Green chemistry tries to use safer molecular oxygen (O2), ozone
(O3), and hydrogen peroxide (H2O2) usually used with a suitable
catalyst or catalyzed by enzymes
• Organisms carry out biochemical oxidations under mild conditions
using monooxygenase and peroxidase enzymes that catalyze the
oxidizing action of molecular oxygen or hydrogen peroxide
Reduction
Reduction consisting of loss of O, gain of H, or gain of electrons
• Hazardous reductants such as lithium aluminum hydride (LiAlH4)
and tributyltin hydride.
Electrical currents can be used for oxidation and reduction without
reagents:
Alkylation
Alkylation for attachment of alkyl groups especially -CH3
• Commonly performed with dimethyl sulfate reagent
O
+ H3C O S O CH3 + 2NaOH
2R N
H
O
CH3
Dimethyl sulfate
2R N
+ Na 2SO4 + 2H 2O
H
H
(11.9.3)
• Dimethyl sulfate may be carcinogenic
• As an alternative, use dimethyl carbonate
H
2R N
H
O
+ H3C O C O CH3
Dimethyl carbonate
H
CH3
2R N
+ CO2 + H C OH
H
H
(11.9.4)
Media
Media in which reactions occur
Usually organic solvents or water
Provide a medium in which feedstocks and reagents can dissolve and
come into close, rapid contact at the molecular level
• Water is safest, but may not work for organic materials
• Hydrocarbon solvents may burn, explode or be toxic
Replace solvents with less hazardous ones, such as benzene (which
may cause leukemia) by toluene
CH3
Benzene
Toluene
Replace straight-chain hydrocarbon n-hexane, which can cause
peripheral neuropathy, with branched-chain 2,5-dimethylhexane,
which is not very toxic
Nonpolar organic solvents suspended as colloidal particles can be
used as media
Supercritical carbon dioxide at high pressure and elevated
temperature can act as media
Ionic Liquids
Ionic liquids such as the one shown below have been used as media
for some reactions:
F
H
H
H
H
+
N
N
F
F
H3C
C C C C H
P
F
F
H H H H
F
1-Butyl-3-methylimidazolium hexafluorophosphate
Solvent-free reactions have been used with some success
Catalysts
Catalysts are substances that speed reactions without being
consumed themselves
Heterogeneous catalysts that are held upon some sort of support
where they interact with reactants
• Readily separated from reaction products
Homogeneous catalysts that are actually mixed with the reactants
• Often work better because of intimate contact with reagents
• Require separation and may contaminate product
An objective of green chemistry is to develop heterogeneous
catalysts that equal homogeneous catalysts in their performance
Enhancement of Catalyst Selectivity
Selectivity enhancement of catalysts is desirable
Lower energy requirements and less severe, safer conditions with
appropriate catalysts
Enzyme-catalyzed green chemical processes including those with
transgenic organisms
Synthetic catalysts that mimic enzyme action such as the one shown
below that mimics iron-based enzymes
Alkene (R is an unspecified
organic group
H
H
N
H
C
C
N
Epoxide group attached by
oxidation at C=C bond
N
Fe
N
O
+ H2O2
H C
R Catalyst of N,N'-dimethyl-N,N'bis(2-pyridylH
methyl)ethylenediamine bonded to Fe
2+
ion
H
C
R